Method of and apparatus for establishing and maintaining dispersions of liquid and gaseous fractions

ABSTRACT

A dispersion of air or oxygen in liquid sewage and/or or sludge is admitted tangentially into the lower portion of an upright vessel wherein the dispersion rises and is compelled to flow through eccentric flow restricting passages in several superimposed horizontal partitions so that the dispersion is repeatedly induced to form a turbulent helical flow. The rising dispersion flows around a tube which returns a portion of the dispersion into the lower part of the vessel and causes the remaining portion to overflow into a receptacle having an outlet at a level below the open top of the tube. The dispersion which descends in the tube is readmitted tangentially into one or more chambers which are separated from each other by the partitions in the vessel and communicate with each other by way of the respective flow restricting passages.

BACKGROUND OF THE INVENTION

The invention relates to a method of and to an apparatus forestablishing and maintaining dispersions of liquid and gaseousfractions, particularly for dispersing oxygen, air and/or otheroxygen-containing gases in liquid sludge and/or sewage. Moreparticularly, the invention relates to improvements in methods andapparatus which can be utilized to carry out biochemical processesinvolving intimate contact of liquid fractions with gaseous fractionsand/or microorganisms in a reactor, preferably in an upright vessel.

It is known to disperse a gaseous fraction in a liquid fraction and tocause the resulting dispersion to flow upwardly in a vessel wherein theliquid fraction is discharged at the top and the spent gaseous fractionwhich becomes separated from the liquid fraction is evacuated at the topindependently of the treated liquid fraction. An apparatus which can beused for the practice of such method is disclosed in German patentapplication Ser. No. P 35 36 057.7. An advantage of such apparatus isthat the period of dwell of the dispersion therein is relatively longeven though the vessel is relatively short. The apparatus of thisapplication comprises an inlet for admission of the dispersion into andsubstantially tangentially of the lower portion of the vessel, and aconduit which returns a portion of or the entire dispersion from theupper portion into the lower portion of the vessel for recirculation,i.e., for longer-lasting contact of the liquid and gaseous fractions.Intensive contact between the liquid and gaseous fractions is ofparticular importance if the apparatus is used as a means for initiatingand promoting biochemical reactions, especially reactions of air and/orother oxygen-containing gases with active biomasses in a liquid medium.Such intensive contact contributes to the economy of the operation byensuring that the treatment is completed within a relatively shortinterval of time and that the admitted gaseous fraction is utilized witha high degree of effectiveness. Moreover, it is relatively simple tomaintain the temperature of the dispersion at an optimum value. All thisis ensured by maintaining the gaseous fraction in desirable intimatecontact with the liquid or liquefied fraction for a sufficiently longinterval of time.

The method and apparatus of the aforementioned German application aresimple and effective. However, it has been found that the path alongwhich the dispersion rises in the vessel is often too short unless theheight of the vessel is unduly increased. This is due to the fact thatfriction-induced deceleration of the dispersion in the vessel entails apronounced reduction of the rate and intensity of circulation already ata level rather close to the inlet of the vessel. Moreover, thedecelerated gaseous and liquid fractions exhibit a pronounced tendencyto become separated from each other. As the tendency of the dispersionto circulate decreases or vanishes, the dispersion begins to flowupwardly along a more or less straight path so that the period of dwellin the vessel and hence the reaction times ar reduced accordingly.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a novel and improved method oftreating a liquid or liquefied fraction with a gaseous fraction in sucha way that the treatment is completed within a relatively short intervalof time and in a relatively small vessel even though the liquid fractioncovers a considerable distance while remaining in intimate contact withthe gaseous fraction.

Another object of the invention is to provide a method which ensuresthat the intensity of reaction between the gaseous and liquid fractionsremains unchanged or fluctuates very little in each and every portion ofthe path wherein the fractions are caused to interact.

A further object of the invention is to provide a simple but highlyefficient method of intimately contacting sewage and/or sludge withoxygen-containing gases and microorganisms.

An additional object of the invention is to provide a method ofrepeatedly inducing an ascending dispersion of gaseous and liquidfractions to flow along a path which deviates from a straight path.

Still another object of the invention is to provide a method whichrenders it possible to subject a liquid fraction to intensive treatmentby intimate contact with a gaseous fraction in a relatively simple andinexpensive apparatus.

A further object of the invention is to provide a novel and improvedapparatus for the practice of the above outlined method.

An additional object of the invention is to provide a novel and improvedvessel for use in the above outlined apparatus and for the practice ofthe above outlined method.

Another object of the invention is to provide the apparatus with noveland improved means for repeatedly inducing a dispersion of gaseous andliquid fractions to flow along an ideal or nearly ideal path while beingconveyed between two levels which are relatively close to each other.

A further object of the invention is to provide novel and improved meansfor subdividing the vessel of the above outlined apparatus and novel andimproved means for influencing the speed and pressure of the conveyedgaseous and liquid fractions.

One feature of the present invention resides in the provision of amethod of treating a liquid fraction with a gaseous fraction,particularly of intimately contacting sewage and/or sludge with airand/or oxygen. The method comprises the steps of dispersing the gaseousfraction in the liquid fraction, conveying the resulting dispersionupwardly along an elongated at least partially helical path through aseries of superimposed chambers, throttling the flow of the dispersionbetween at least two superimposed chambers, damming the flow of thedispersion in the region of the upper end of the path, dividing (atleast at intervals) the dammed dispersion into first and second streams,returning one of the streams into or close to the lower end of the path,and evacuating the other of the streams from the upper end of the path.The method preferably further comprises the steps of interrupting theupward flow of the dispersion between the two superimposed chambers andthrottling the flow of the dispersion in the region of the upper end ofthe path simultaneously with or immediately preceding the dividing step.The returning step can include conveying the one stream downwardly alonga second path which is surrounded by the elongated path. The otherstream can be temporarily stored in a receptacle on top of the elongatedpath prior to the evacuating step.

The first throttling step can include throttling the upward flow of thedispersion between several superimposed chambers.

The conveying step can include maintaining the dispersion (e.g., bymeans of a pump) at an elevated pressure, and the first throttling stepcan include raising the pressure of the dispersion in the lower chamberof the two chambers.

In accordance with a presently preferred embodiment of the method, theconveying step includes inducing the dispersion to rise within anupright vessel having a housing or shell which is tubular at least inthe region of the upper chamber of the two superimposed chambers, andthe first throttling step preferably comprises placing between the twosuperimposed chambers a substantially horizontal partition and providingthe partition with at least one passage which induces an at leastsubstantially horizontal flow of the dispersion from the lower chamberinto the upper chamber of the two superimposed chambers andsubstantially tangentially of the shell.

The first throttling step can include throttling the upward flow of thedispersion between a plurality of additional superimposed chambers at alevel above the lower chamber of the aforementioned pair of superimposedchambers and at angularly offset locations of the path, e.g.,diametrically opposite each other with reference to the axis of thevessel. The first throttling step then further comprises placingsubstantially horizontal partitions between superimposed chambers andproviding the partitions with flow restricting passages which induce asubstantially horizontal flow of the dispersion, at least immediatelyabove the respective partitions.

The returning step can include admitting at least a portion of the onestream into at least one of the chambers. The admission preferably takesplace at the level or at levels close to and above the partition orpartitions in the vessel and preferably tangentially or nearlytangentially of the respective portion of the shell.

The gaseous fraction forms bubbles which rise in the path at apredetermined speed. The conveying and throttling steps are preferablyselected and/or regulated in such a way that the dispersion ismaintained at an elevated pressure which suffices to ensure that theupward flow of the dispersion takes place at a speed exceeding thepredetermined speed.

The pressure of the dispersion can be reduced in the upper portion ofthe path upon completion of the dividing step; at least the other streamis then circulated to accelerate such other stream prior to theevacuating step (this entails a separation of the gaseous fraction sothat the evacuating step can include evacuation of liquid fraction aloneor of a liquid fraction with a relatively low percentage of gaseousfraction therein).

The method can also comprise the step of confining a carrier materialfor microorganisms in at least one of the chambers so that the ascendingdispersion is caused to intimately contact the microorganisms.

Another feature of the present invention resides in the provision of anapparatus for treating a liquid fraction with a gaseous fraction,particularly for intimately contacting liquid sewage and/or sludge withair and/or oxygen. The apparatus comprises an upright vessel with ahousing or shell having a lower portion, an upper portion and at leastone partition dividing the interior of the vessel into an upper chamberand a lower chamber. Such chambers are located between the upper andlower portions of the vessel, and the partition has at least one flowrestricting or throttling passage. The lower portion of the vessel hasan inlet and the upper portion of the vessel has an outlet, and theapparatus further comprises means (e.g., a venturi) for admitting intothe inlet a dispersion of liquid and gaseous fractions at a pressuresuch that the dispersion rises in the vessel toward the outlet and flowsthrough the passage. The passage is oriented and dimensioned in such away that it imparts to a portion at least of the flow of dispersion asubstantially helical shape, i.e., the rising dispersion flows along anelongated path which includes at least one helical portion. The vesselpreferably further comprises means for damming the flow of dispersion inthe upper portion of the vessel, and the apparatus further comprises areturn conduit having an intake in the upper portion of the vessel, adischarge end in the lower portion of the vessel and at least oneopening for admission of the dispersion from the upper portion of thevessel into the conduit in the region of the damming means.

The vessel can further comprise one or more additional substantiallyhorizontal partitions and additional flow restricting passages in suchadditional partitions so as to repeatedly induce a helical flow of therising dispersion. The partitions are disposed at different levels andare preferably equidistant from each other. Each passage is or can bedefined by a substantially tubular flow-restricting member, and eachsuch member preferably extends substantially tangentially of theadjacent tubular portion of the shell. Each flow-restricting member ispreferably located in the upper one of two neighboring chambers whichare separated from each other by the respective partition, and eachtubular member is or can be adjacent the corresponding tubular portionof the shell.

The apparatus can further comprise conduits or like means for divertingdispersion from the aforementioned return conduit into at least one ofthe chambers. Each diverting means has an outlet which is preferablyadjacent the upper side of the partition beneath the respective chamber.The return conduit can include an upright pipe which is surrounded bythe shell of the vessel, preferably in such a way that the pipe isconcentric with the shell.

The damming means can include a horizontal or nearly horizontal top wallwhich is disposed at least slightly above and is preferably close to theintake of the return conduit. The return conduit can be provided withone or more inwardly extending nipples each of which defines an intakefor admission of dispersion from the upper portion of the vessel intothe return conduit. Each nipple can be disposed substantiallytangentially of the return conduit.

The upper portion of the vessel can include an enlarged receptacle abovethe damming means, and the return conduit preferably extends upwardlyand above the damming means and has an open top so that the dispersioncan overflow into the receptacle. The outlet in the upper portion of thevessel is then provided in the receptacle at a level below the open topof the return conduit.

Each partition can include a washer-like plate or panel which issealingly secured to the return conduit and to the shell.

The admitting means can include or can cooperate with one or more pumpswhich can maintain the dispersion, even in the region of the dammingmeans, at a speed of approximately ten meters per second in spite of theprovision of one or more flow restricting passages between the inlet inthe lower portion of the vessel and the damming means.

The apparatus can further contain carrier material for microorganisms inat least one of the chambers, and the admitting means is preferablyarranged to induce the dispersion to flow at a speed such that thecarrier material remains in the one chamber (i.e., that it does not flowinto the chamber or chambers above the one chamber or into the outlet)while the microorganisms on such carrier material are being contactedwith the rising and circulating dispersion.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic central vertical sectional view of an apparatuswhich embodies one form of the invention;

FIG. 2 is a plan view of a partition in the vessel of the apparatuswhich is shown in FIG. 1; and

FIG. 3 is a plan view of a top wall constituting a damming means in theupper portion of the upright vessel of the apparatus which is shown inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus which is shown in FIG. 1 comprises an upright vessel 1having a tubular (preferably at least partly cylindrical) housing orshell 9 with a lower portion 4, and upper portion 11 and a plurality ofsuperimposed chambers 30 separated from each other by horizontalpartitions 7 of the type shown in FIG. 2. The apparatus can be used as areactor to carry out biochemical processes, e.g., to intimately contactliquid or liquefied sludge or sewage with pure oxygen, with air or withanother oxygen-containing gas. The gaseous fraction is supplied at 3from a suitable source, not shown, and the liquid fraction is suppliedat 29a, again from a source which is not shown in the drawing. The means3a for admitting a dispersion of the gaseous fraction in the liquidfraction into the lower portion 4 of the shell 9 (namely into an inlet25 which is disposed substantially tangentially of the shell to induce acirculation of the admitted dispersion 2 while the dispersion rises inthe vessel 1) can comprise a venturi or the like and a pump (as at 29a)which causes the dispersion to enter the vessel 1 at an elevatedpressure. The upper portion 11 of the vessel 1 includes a radiallyenlarged receptacle 22 having a top wall with an opening or outlet 6 forevacuation of gaseous fraction which has become separated from thedispersion 2. The receptacle 22 is further provided with an outlet 23which serves for evacuation of some of the dispersion 2 which has risenin the shell 9 from the inlet 25 through successive chambers 30 andultimately into the receptacle 22.

The rising dispersion 2 flows along an elongated substantially helicalpath which surrounds an upright return conduit 13 (hereinafter calledtube for short). The tube 13 is preferably concentric with the shell 9and its top is open, as at 24, and extends above a top wall 14 which isprovided in the upper portion 11 of the vessel 1 beneath the receptacle23 and serves as a means for damming the flow of rising dispersion 2 sothat the dispersion ceases to flow upwardly and is compelled to enterthe upper portion of the tube 13 by way of one or more (e.g., two, seeFIG. 3) substantially tangentially extending nipples 12 definingthrottling orifices at a level slightly beneath the top wall or dammingmeans 14.

The rising dispersion 2 is caused to flow along a helical path becausethe inlet 25 is designed to admit a stream of dispersion substantiallytangentially of the lower portion 4. In addition, each of the horizontalpartitions 7 defines a passage 8 which extends substantiallytangentially of and is adjacent the internal surface of the respective(tubular) portion of the shell 9 so that the tendency of the dispersion2 to flow along a helical path is enhanced at several levels between theinlet 25 and the top wall 14. The passages 8 are defined bysubstantially horizontal tubular throttling or flow restricting members10 in the form of relatively short elbows which are disposed at levelsabove the respective partitions 7. Each such partition actuallyinterrupts the upward flow of the major portion of the body ofdispersion in the shell 9, and the dispersion is then compelled to flowin the respective passage 8 in a manner as indicated by the solid-linearrow in FIG. 2, i.e., close to and along the internal surface of theshell 9 and circumferentially of the tube 13. Such repeated inducementof the dispersion 2 to flow along a helical path prolongs the period ofdwell of the dispersion in the vessel 1 and ensures that the treatmentcan be completed even if the vessel is relatively short. The featurethat the passages 8 which are defined by the flow restricting orthrottling members 10 do not merely provide simple openings for thedispersion 2 but compel the dispersion to flow circumferentially of andaround the tube 13 ensures that the path along which the dispersionflows from the inlet 25 to the top wall 14 is surprisingly long eventhough the distance between the levels of the inlet 25 and the top wall14 is rather short. It will be noted that the partitions 7 and theirflow restricting members 10 perform several important functions, namelyof repeatedly interrupting the upward flow of the dispersion 2 as wellas of repeatedly inducing the dispersion to flow along a helical pathrather than simply vertically or nearly vertically upwardly.

The pressure at which the dispersion 2 is admitted into the lowerportion 4 of the vessel 1 is preferably such that the dispersion isstabilized, i.e., that the gaseous fraction does not tend to becomesegregated from the liquid fraction. The application of such relativelyhigh pressure also contributes to the possibility of completing thetreatment of the liquid fraction in a relatively short vessel. Thepressure in the vessel 1 is further increased by the partitions 7 eachof which defines a relatively small passage 8 for the flow of dispersionfrom the respective lower chamber into the respective upper chamber 30.Each partition 7 acts not unlike the top wall or damming means 14 exceptthat the latter does not define a passage for direct flow of thedispersion from the topmost chamber 30 into the receptacle 22. Instead,the dispersion must pass though the nipples or nozzles 12 and mustoverflow the open top 24 of the tube 13. The operator of the apparatuscan simulate a water column of any desired height by simply increasingor reducing the rate of admission of dispersion into the inlet 25, i.e.,by selecting the pressure of dispersion in the shell 9 of the vessel 1.The pressure of dispersion 2 is reduced, particularly to atmosphericpressure, in the receptacle 22.

It is preferred to provide the vessel 1 with a relatively large numberof partitions 7 and to install the neighboring partitions at the samedistance from each other. This ensures that the rising dispersion 2 isrepeatedly induced to flow along a helical path at several levels whichare uniformly spaced apart from each other between the upper and lowerportions 11 and 4 of the vessel 1. At the same time, the partitions 7repeatedly interrupt the upward flow of the dispersion and ensure thatthe dispersion is repeatedly subjected to an effective flow-restrictingaction, i.e., while flowing through successive passages 8 on its wayfrom the inlet 25 toward and into the throttling orifices which aredefined by the nipples 12 in the upper portion of the tube 13. It willbe seen that the dispersion is repeatedly throttled by the partitions 7and that the dispersion which has risen above the topmost partition 7 isthrottled again while flowing from the upper portion 11 of the shell 9into the upper portion of the tube 13 by way of the nipples 12. Theflow-discharging portions of the elbow-like flow restricting members 10are preferably horizontal and are preferably closely adjacent the uppersides of the respective partitions 7 so as to ensure that the lowermost"helix" of dispersion in each chamber 30 is located in or close to ahorizontal plane and that the body of dispersion in each chamber 30 canform several superimposed "helices" before reaching the underside of thepartition 7 above such chamber or the top wall 14.

The tendency of the dispersion 2 to circulate in the chambers 30 can beenhanced still further by providing some or all of the partitions 7 withpairs of three or more circumferentially spaced-apart passages 8.

That stream of the dispersion 2 which enters the upper portion of thetube 13 by way of the nipples 12 and flows downwardly is returned intothe lower portion of the path for the rising dispersion by a pump 16which draws the dispersion from the lower portion 15 of the tube 13 byway of a conduit 29 and diverts at least some of the thus withdrawndispersion into conduits 17, 18 and 19 which respectively admit streamsor streamlets of dispersion substantially tangentially of the shell 9into the lower portion 4 (this lower portion can be said to constitutethe lowermost chamber in the interior of the shell 9), into the chamber30 above the lowermost partition 7, and into the chamber 30 above thenext-to-the-lowermost partition 7. Such streams or streamlets ofdispersion are admitted close to the upper sides of the respectivepartitions (the bottom wall of the vessel 1 can be said to constitute apartition beneath the lower portion or chamber 4) and they enhance thetendency of dispersion 2 to flow along a helical path while ascendingfrom chamber to chamber to ultimately enter the upper portion of thetube 13. Recirculation of some or all of the stream which flowsdownwardly in the tube 13 contributes to a further significant extensionof the period of intimate contact between the liquid and gaseousfractions of the dispersion.

The number of chambers which receive recirculated dispersion can bereduced to two or one or increased to four or more.

A substantial percentage of gaseous fraction is caused to becomeseparated from the liquid fraction during flow through the orificeswhich are defined by the nipples 12 in the upper portion of the tuber13. This is due to the fact that the cross-sectional area of eachorifice is relatively small and that such orifices are formed in part byarcuate guide means or baffles 20 which extend circumferentially alongthe internal surface of the tube 13 and cause the dispersion whichenters the upper portion of the tube to circulate at an elevated speedwith attendant pronounced segregation of liquid and gaseous fractionsunder the action of centrifugal force. The gaseous fraction rises in thereceptacle 22 and is evacuated by way of the outlet 6. Thus, the streamwhich descends in the tube 13 contains a relatively small percentage ofgaseous fraction. The outlet 6 can admit the segregated gaseous fractioninto a suitable cleaning, filtering or like unit, not shown.

The number of helices which are described by the dispersion 2 duringflow from the inlet 25 to the flow-restricting nipples 12 in the upperportion of the tube 13 (and hence the average reaction time) can beregulated in a number of different ways, for example, by varying therate of admission of untreated dispersion via inlet 25 and/or by varyingthe rate of admission of partially treated dispersion into one or morechambers 30 by way of the respective conduit or conduits 17, 18, 19. Theheight of the column of dispersion in the tube 13 rises in response toincreasing rate of admission of untreated dispersion via inlet 25. Thereceptacle 22 can receive dispersion only when such dispersion overflowsthe open top 24 of the tube 13. The conduit which is connected to theoutlet 23 evacuates all of the dispersion which overflows into thereceptacle 22.

If the column of dispersion in the tube 13 does not reach the open top24 and the admission of untreated dispersion via inlet 25 isinterrupted, the dispersion which happens to be confined in the vessel 1is or can be recirculated once, twice or more than twice, i.e., as oftenas desired. Such dispersion is pumped at 16 into the conduits 17-19 toenter the respective chambers and to rise in the space around the tube13 in order to enter the tube via nipples 12 and to return into thelower portion 15 of the tube, i.e., into the range of the pump 16.

On the other hand, if the inlet 25 continuously receives a stream offresh (untreated) dispersion, a stream of dispersion continuouslyoverflows the open top 24 of the tube 13 and is evacuated from thereceptacle 22 via outlet 23 which, as explained above, is located at alevel below the open top 24. The average period of dwell of dispersionin the apparatus can be regulated by varying the rate of admission offresh dispersion via inlet 25.

In order to reduce the likelihood of foaming, the receptacle 22preferably contains a spray pipe 26 which is disposed close to the topof the receptacle and receives dispersion from the upper portion 11 byway of a supply conduit 27. The tendency of the dispersion to form ismost pronounced in the region of the open top 24 of the tube 13, i.e.,where the segregated gaseous fraction ascends in the receptacle 22 onits way toward the outlet 6. The tendency of ascending gaseous fractionto cause foaming is drastically reduced by sprays of dispersion whichare discharged by the orifices of the pipe 26 and descend on top of thebody of dispersion in the receptacle 22. The pressure in the upperportion 11 of the vessel 1 (beneath the top wall 14) is sufficientlyhigh to ensure that the conduit 27 can supply the orifices of the spraypipe 26 with a continuous stream of dispersion.

The interruption of upward flow of the dispersion 2 by each partition 7ensures that the gaseous fraction does not become separated from theliquid fraction, even if the circulation velocity of the risingdispersion is relatively low. Moreover, throttling of the flow ofdispersion 2 on its way through the flow restricting members 10 of thepartitions 7 ensures that the pressure of the dispersion in the chamberbeneath each member 10 rises to counteract an increasing coalescence andto thus stabilize the dispersion. Such mode of treating the dispersionensures that the period of dwell of gaseous fraction in the dispersionis much longer than when the dispersion is free to flow freely in areactor vessel. Moreover, each partition 7 brings about a renewedintimate mixing of the gaseous and liquid fractions. This, too, enhancesthe quality of treatment of the liquid fraction and allows forrelatively rapid completion of treatment in a compact apparatus. Asmentioned above, the period of dwell of dispersion 2 in the vessel 1 canbe increased practically at will by the simple expedient of shutting offthe admission of fresh dispersion and by recirculating the dispersion inthe apparatus by the pump 16 and conduits 17-19 as often as desired.

The energy which is required to effect a circulation of dispersion assoon as the dispersion enters the lower portion of a chamber 30 issupplied as a result of the establishment of elevated pressure in theupper portion of each chamber 30, i.e., beneath each partition 7. Thepotential energy in the form of pressure is converted into kineticenergy as a result of the flow of dispersion through the passages 8which are defined by the flow restricting members 10, i.e., the velocityof the dispersion increases as soon as the dispersion leaves a lowerchamber. The increase of velocity is limited to the lower portion of thenext-higher chamber, i.e., to the region immediately or closely above apartition 7. The aforediscussed configuration of the flow restrictingmembers 10 (namely the configuration which ensures that the initial flowof the dispersion which enters the lower portion of a chamber 30 ishorizontal or nearly horizontal) and the aforediscussed orientation ofthe members 10 (so that the flow is substantially tangential to theadjacent tubular portion of the shell 9) ensure that the flow of thedispersion is circular and that the rising dispersion flows along ahelical path which is much longer than the shortest distance between theinlet 25 and the nipples 12. Repeated infusion of energy which is usedto bring about a circulatory movement of the dispersion ensures thatsuch circulatory movement takes place all the way between the inlet 25and the upper portion of the tube 13 with minor interruptions in theregions of the partitions 7. As mentioned above, the partitions 7 can beprovided with several suitably distributed passages to further enhancethe tendency of the rising dispersion to flow along a helical path. Forexample, at least one partition 7 can be provided with two passages 8which are disposed diametrically opposite each other with reference tothe axis of the tube 13. The provision of two or more passages in one ormore partitions 7 renders it possible to achieve a desired circulationof the dispersion while the speed of the dispersion which issues fromthe passages is lower than in the case of partitions having a singlepassage. This enhances the uniformity of the circulating dispersion. Thenumber of passages 8 in each partition 7 (or in some of the partitions)can be increased to three or more.

The purpose of the throttling action of nipples 12 beneath the top wall14 is to further prolong the interval of intimate contact between thegaseous and liquid fractions. Such intervals can be lengthened stillfurther by recirculating the treated dispersion by way of the tube 13,pump 16, one or more diverting conduits (17-19) and chambers 30 back tothe nipples 12. Thus, the average period of dwell of the dispersion inthe apparatus including the vessel 1 can be varied within a very widerange (e.g., between 4 and 12 minutes). The operators can furthercontrol the quantity of recirculated dispersion, e.g., by reducing orincreasing the throughput of the pump 16 and/or by closing the valve(not shown) in one or more diverting conduits (17-19). Moreover, theoperator or operators can control the timing of recirculation of thedispersion by starting or stopping the pump 16. All this enables theoperator or operators to optimize the treatment of the liquid fraction,the output of the apparatus, the energy consumption of the apparatus,the efficiency of utilization of the gaseous fraction, the efficiency ofutilization of reaction promoting microorganisms and/or chemicals in thevessel 1 and/or other variables.

An important advantage of the improved apparatus is that repeatedcirculation of the dispersion on its way from the inlet 25 into theupper portion of the tube 13 is achieved in a very simple andinexpensive way, i.e., by the simple expedient of installing one or morepartitions 7 with suitably dimensioned and oriented passages 8 whereinthe flow of dispersion is throttled and which ensure that the dispersionbegins to circulate around the tube 13 as soon as it enters the lowerportion of a chamber above a partition. The number of partitions will beselected as a function of frictional losses and in dependency on thedimensions of the apparatus.

The illustrated straight tube 13 can be replaced with an otherwiseconfigurated tube without departing from the spirit of the invention. Astraight cylindrical tube is preferred because of its lower cost andsimplicity of installation. The diameter of the tube 13 can be betweenone-third and one-fourth the diameter of the shell 9. Such dimensioningof the tube 13 has been found to exert a beneficial effect upon the flowof dispersion 2 in the chambers which surround the tube and are, inturn, surrounded by the shell 9. The utilization of a tube 13 having arelatively large diameter is desirable and advantageous because thiscontributes to more satisfactory circulation of dispersion in thechambers 30. The reason is that the rate of circulation at the verycenter of a chamber 30 (in the absence of the tube 13) or close to suchcenter would be very low and could even adversely affect the overallflow of dispersion from the inlet 25 to the region immediately beneaththe top wall 14. Were the tube 13 placed outside of the shell 9 or ifthe tube 13 were omitted altogether, the dispersion 2 could develop apronounced upward flow in the central region of the shell 9 which wouldresult in a less satisfactory treatment or could even result ininsufficient treatment of some or all of the dispersion. Such problemsare avoided by the simple expedient of utilizing a large-diameter tube13.

The provision of seals between the radially innermost portions of thepartitions 7 and the tube 13 on the one hand, and the peripheralportions of partitions 7 and the shell 9 on the other hand, ensures thatthe entire dispersion is compelled to flow through the passages 8 and isthus set in a circular motion as soon as it enters the lower portion ofthe next higher chamber. The partitions 7 further serve to act assupports or platforms for carrier material of microorganisms which canbe used in the apparatus to promote the treatment of the liquidfraction. Such carrier material accumulates on the partitions when theapparatus is idle. Thus, the partitions prevent the carrier materialfrom descending from chamber to chamber when the inlet 25 does notreceive fresh dispersion and/or when the pump 16 is idle and the conduit17, 18 and/or 19 does not admit pretreated dispersion into therespective chamber or chambers.

The diameter of the tube 13 is or can be constant from end to end. Thisis particularly desirable and advantageous in the upper part of the tubebecause such dimensioning enhances the separation of gaseous fractionfrom the liquid fraction of dispersion which enters the upper portion ofthe tube 13 and is accelerated and caused to circulate at a relativelyhigh speed as a result of the dimensioning, orientation and location ofthe nipples 12 which provide orifices for the flow of dispersion fromthe region immediately below the top wall 14 into the tube 13. Thedimensions of the orifices in the nipples 12 can be readily selected insuch a way that the dispersion which enters the upper portion of thetube 13 begins to circulate at a relatively high speed which issufficient to ensure that the action of centrifugal force suffices tobring about extensive separation of gaseous and liquid fractions, i.e.,bubbles of the gaseous fraction will rise in the tube 13 toward and intothe outlet 6 in the top portion of the receptacle 22. It is clear thatsegregation of gaseous and liquid fractions can be carried out in aseparate container. The structure which is shown in the drawing (andwherein the segregation of gaseous fraction takes place in the upperportion of the tube 13) is preferred at this time because it contributesto simplicity, compactness and lower cost of the apparatus.

As mentioned above, the number of times a batch of dispersion 2 isrecirculated in the apparatus can be selected practically at will byappropriate adjustment of the rate of admission of fresh dispersion viainlet 25 (or by interrupting the admission of fresh dispersion), byregulating the operation of the pump 16 and/or by selecting the numberof diverting conduits which admit pretreated dispersion into thecorresponding chamber or chambers as well as by selecting the rate offlow of dispersion in the selected diverting conduit or conduits.

The reaction velocity in various portions of the vessel 1 depends, to aconsiderable extent, upon the degree of concentration of microorganisms.In order to promote the reaction, one or more chambers or portions ofthe vessel 1 can contain a carrier material 28 (indicated schematicallyby broken horizontal lines) the surface of which carries a film or layerof microorganisms which can be said to form a microbiological lawn. Suchmicroorganisms are available for uninterrupted treatment of thedispersion 2 which rises in the shell 9. The rate of upward flow of thedispersion is preferably selected in such a way that the carriermaterial 28 remains in the respective chamber or chambers, i.e., thecarrier material is not caused to rise into the next-higher chamber ordescend into the chamber below. In other words, the circulatingdispersion is maintained in intimate contact with the microorganismswhich are carried by the material 28 in the respective chamber orchambers. Each partition 7 is a washer-like panel the innermost portionof which is sealingly connected with the tube 13 and the peripheralportion of which is sealingly connected with the sell 9 so that the onlypath for the flow of dispersion 2 from chamber to chamber is by way ofthe respective passage 8. As mentioned above, the rate of upward flow ofthe dispersion and the cross-sectional areas of the passages 8 are orcan be selected in such a way that the carrier material 28 remainsconfined in the respective chamber wherein it can float between theupper side of the partition 7 below the passage 8 above. It will be seenthat, in addition to the aforediscussed functions, the partitions 7 alsoserve as a means for confining the carrier material 28 in the respectivechambers.

Introduction of carrier material 28 for microorganisms into one or morechambers 30 is of particular importance in apparatus wherein the activebiological material includes gradually growing microorganisms and/ormicroorganisms which can be readily washed away. Examples of suchmicroorganisms are nitrogen-fixing bacteria or methane-forming bacteria.In contrast to heretofore known processes of such character, known asfluidized-bed or vibrating-layer methods, it is now proposed to impart;to the entire carrier material 28 and to the microorganisms thereon acirculatory movement as a result of the flow of dispersion 2 along ahelical path, to retain the carrier material 28 in the respectivechamber or chambers of the vessel 1, and to ensure that differencesbetween the densities of carrier material and reaction product do notallow the carrier material to rise into the next-higher chamber orchambers. This ensures the establishment of a large surface-to-surfacecontact between the dispersion 2 and the microorganisms as well as ahighly satisfactory intermixing of dispersion with the microorganisms.All this is achieved while the carrier material 28 remains confined tocirculatory movements in the selected chamber or chambers of the vessel1.

The metabolism of the microorganisms entails their growth on theparticles of carrier material 28. Nevertheless, the aforediscussed modeof circulating the carrier material 28 in the selected chamber orchambers prevents the development of an excessively thick layer ofmicroorganisms. One of the reasons for the prevention of development ofoverly thick layers is that the circulating particles of carriermaterial 28 rub against each other to thereby segregate and liberate acertain percentage of microorganisms. The segregated microorganismsconstitute a freely flowing biological material having a specific weightwhich is much lower than that of the carrier material and/or of carriermaterial plus the microorganisms adhering thereto. Consequently, thethus liberated biological material is free to rise with the dispersionthrough the passages 8 of the partitions 7 and to ultimately enter thetube 13. Such self-cleaning action has been found to ensure thethickness of layers of microorganisms on the particles of carriermaterial 28 does not exceed an optimum value. Moreover, the segregatedbiological material is highly unlikely to clog the narrow passages 8 butis permitted to remain in long-lasting contact with the ascending flowof dispersion 2. The result is a surprisingly pronounced rise ofreaction velocity because the microorganisms are in continuous intensiveand large-area contact with the dispersion.

The carrier material 28 can consist of or can contain granular activatedcarbon, sand, brown coal, pellets of coke, anthracite or the like with aparticle size of 0.2 to 3 mm.

The circulation velocity of the dispersion 2 is or can be selected independency on the density of introduced carrier material 28 so as toensure that such material will circulate in the selected chamber orchambers without accumulating on the partition or partitions 7therebelow and will not rise into the next-higher chamber or chambers.Thus, the helices of rising dispersion traverse the circulating carriermaterial on their way from a lower passage 8 into a higher passage withthe resulting intimate contact between the dispersion and themicroorganisms.

The biochemical reactions in the vessel 1 can be enhanced still furtherto a considerable extent by introducing different types ofmicroorganisms into different chambers and by properly relating theselected microorganisms to the stages of treatment to which the risingflow of dispersion 2 has already been subjected on its way into aparticular chamber. This ensures that the microorganisms in thecorresponding chambers can optimize the respective biochemicalconversion stage as determined by the function working relationship atthe corresponding level of the vessel. To this end, the conditions forthe growth of particular bacteria in various chambers of the vessel 1can be optimized by appropriate selection of the concentration ofgaseous fraction, temperature, extent of agitation of the dispersion andother parameters so as to ensure an optimizing of reactions betweenbacteria and the dispersion in the corresponding chambers. Thus, theaforediscussed subdivision of the interior of the vessel 1 into a seriesof superimposed chambers brings about the additional advantage that thebiochemical conversion process can be regulated with a high degree ofaccuracy and in a simple, inexpensive and highly efficient way. Theoptimizing of circumstances for the existence and growth of one or moretypes of microorganisms in selected chambers of the vessel entails anoptimizing of the biochemical activity of the microorganisms and hencean optimum treatment of the liquid fraction in a relatively short vesseland within a relatively short interval of time. Moreover, and eventhough the carrier material 28 is free (and actually compelled) tocirculate in the selected chamber, the individual cultures ofmicroorganisms remain confined in the respective chambers with theexception of those which are released by the particles of carriermaterial 28 as a result of the aforediscussed frictional engagementbetween neighboring particles of carrier material.

The selection of optimum conditions for the growth of microorganisms inone or more chambers can be effected in a relatively simple andinexpensive way. For example, the temperature in a selected chamber canbe raised by the simple expedient of surrounding the respective portionof the shell 9 with an insulating layer or by dispensing with thecooling of such portion of the shell so that heat which is generated asa result of reactions in the respective chamber or chambers entails anautomatic heating of the dispersion and microorganisms in thecorresponding chamber or chambers. The percentage of gaseous fraction ina particular chamber can be regulated by the admission of controlledquantities of partially or fully treated dispersion by way of theconduit 17, 18, 19. Moreover, the nutritive substatum for microorganismsin a particular chamber can be optimized by introducing into therespective chamber a dispersion which has already undergone one or moreprevious treatments (such pretreated dispersion is also admitted viaconduit 17, 18 and/or 19).

The carrier material 28 is preferably porous so that the microorganismscan settle in its pores and are less likely to be washed away into thenext-higher chamber or chambers when the apparatus is in actual use. Thefeature that the carrier material 28 is caused to circulate in therespective chamber or chambers is desirable and advantageous becausethis ensures that the dispersion in each and every portion of suchchamber is in continuous contact with the microorganisms as long as itremains in the respective chamber or chambers. Moreover, this entails amore effective and more rapid utilization of the gaseous fraction.Uniform distribution of gaseous fraction in the dispersion, coupled withstabilized circulation of the dispersion in the chambers of the vesseland with uniform action of microorganisms upon each portion of thedispersion in the respective chamber, ensures an optimum treatment ofthe dispersion within a short period of time and in a small apparatus.

It has been found that the improved method can be carried out with ahigh degree of efficiency in an apparatus employing a vessel 1 with aheight of up to 8 meters and an overall diameter of not more than 4meters. The partitions 7 can be installed at 1-2 meter intervals. It wasfurther found that the operation of the apparatus is quite satisfactoryif the velocity of the rising dispersion 2 is selected with a view toensure that the rate of flow of dispersion from the space beneath thetop wall 14 into the non-pressurized interior of the tube 13 isapproximately 10 meters per second. This results in segregation of adesired percentage of gaseous fraction which then rises in thereceptacle 22 to be evacuated by way of the outlet 6. The just describedspeed of the dispersion which enters the upper portion of the tube 13further ensures that the circulation velocity of the dispersion 2, evenin the upper portion 11 of the vessel 1, exceeds the speed at whichbubbles of gaseous dispersion rise in the vessel. In order to satisfysuch requirement, the helical path for the dispersion between the inlet25 and the nipples 12 is much longer than the shortest distance betweensuch inlet and the upper portion of the tube 13. The just mentionedselection of the speed of flow of the dispersion ensures that thegaseous fraction can remain in intimate and longlasting contact with theliquid fraction within a relatively short vessel and with much betterresults than if the dispersion were permitted to flow, withoutobstructions, along an upwardly or downwardly extending path.

It was further discovered that a highly satisfactory period of dwell ofdispersion 2 in the vessel 1 is between 4 and 12 minutes. This meansthat the overall volume of dispersion which is treated per unit of time(60 minutes) is between 5 and 15 times the capacity of the apparatus.However, it is clear that the period of dwell can be shortened to lessthan 4 minutes or raised above 12 minutes, depending on the nature ofthe dispersion and upon the desired nature and extent of treatment. Theperiod of dwell of dispersion can be selected with a view to ensure anoptimum utilization of the gaseous fraction and/or to ensure that themethod can be practiced while the concentration of the reactive gasremains within a desired range.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of our contributionto the art and, therefore, such adaptations should and are intended tobe comprehended within the meaning and range of equivalence of theappended claims.

We claim:
 1. A method of treating a liquid fraction with a gaseousfraction, comprising the steps of dispersing the gaseous fraction in theliquid fraction; conveying the resulting dispersion upwardly along anelongated at least partially helical path through a series ofsuperimposed chambers; a first throttling step of throttling the flow ofthe dispersion between at least two superimposed chambers; interruptingthe upward flow of the dispersion between said two superimposedchambers; damming the flow of the dispersion in the region of the upperend of said path; at least intermittently dividing the dammed dispersioninto first and second streams; a second throttling step of throttlingthe flow of the dispersion in the region of the upper end of the pathsimultaneously with or immediately preceding said dividing step;returning one of the streams into the lower end of said path, includingconveying the one stream downwardly along a second path which issurrounded by said elongated path; and evacuating the other of saidstreams from the upper end of said path.
 2. The method of claim 1,further comprising the step of temporarily storing the other streamprior to said evacuating step.
 3. The method of claim 1, wherein saidfirst throttling step includes throttling the upward flow of thedispersion between several superimposed chambers.
 4. The method of claim1, wherein said dispersion conveying step includes maintaining thedispersion at an elevated pressure, said throttling step includingraising the pressure of the dispersion in the lower chamber of said atleast two superimposed chambers.
 5. The method of claim 1, wherein saiddispersion conveying step includes inducing the dispersion to risewithin an upright vessel having a shell which is tubular at least in theregion of the upper chamber of said at least two superimposed chambers,said first throttling step including placing between said at least twochambers a substantially horizontal partition and providing thepartition with at least one passage which induces an at leastsubstantially horizontal flow of the dispersion from the lower chamberinto the upper chamber of said at least two superimposed chambers andsubstantially tangentially of the shell.
 6. The method of claim 1,wherein said first throttling step includes throttling the upward flowof the dispersion between a plurality of additional superimposedchambers at a level above the lower chamber of said at least one pair ofchambers and at angularly offset locations of the path.
 7. The method ofclaim 6, wherein said first throttling step further includes placingsubstantially horizontal partitions between superimposed chambers andproviding the partitions with flow restricting passages which induce asubstantially horizontal flow of the dispersion above the respectivepartitions.
 8. The method of claim 1, wherein said returning stepincludes admitting at least a portion of the one stream into at leastone of said chambers.
 9. The method of claim 8, wherein said firstthrottling step includes installing partitions between neighboringchambers of said series of chambers, said admitting step includingintroducing said portion of the one stream at a level above at least oneof the partitions and substantially tangentially of the respectivechamber.
 10. The method of claim 1 wherein the gaseous fraction formsbubbles which rise in the dispersion at a first speed, said dispersionconveying step and said first throttling step including maintaining thedispersion at an elevated pressure such that the speed of the dispersionin said path exceeds said first speed.
 11. The method of claim 1,further comprising the steps of maintaining the dispersion in said pathat an elevated pressure, reducing the pressure of the dispersion uponcompletion of said dividing step, and circulating at least the otherstream of the dispersion to accelerate such other stream prior to saidevacuating step.
 12. The method of claim 1, further comprising the stepof confining a carrier material living microorganisms thereon in atleast one of said chambers so that the ascending dispersion is caused tointimately contact the microorganisms.
 13. Apparatus for treating aliquid fraction with a gaseous fraction, comprising an upright vesselhaving a lower portion, an upper portion and at least one partitiondividing the interior of the vessel into an upper and lower chamberbetween said upper and lower portions, said partition having at leastone flow restricting passage, said lower portion having an inlet andsaid upper portion having an outlet; means for admitting into said inleta dispersion of liquid and gaseous fraction at a pressure such that thedispersion rises in said vessel and flows through said passage, saidpassage being oriented to impart to a portion at least of the flow ofdispersion a substantially helical shape and said vessel furthercomprising means for damming the flow of dispersion in aid upperportion; and a return conduit having an intake in said upper portion, adischarge end in said lower portion and at least one opening foradmission of dispersion into said intake in the region of said dammingmeans.
 14. The apparatus of claim 13, wherein said vessel furthercomprises at least one additional substantially horizontal partition andan additional flow restricting passage in said additional partition. 15.The apparatus of claim 14, wherein said vessel further comprises aplurality of additional partitions with flow restricting passages, saidpartitions being substantially equidistant from each other intermediatethe upper and lower portions of said vessel.
 16. The apparatus of claim13, wherein said vessel further comprises a tubular flow restrictingmember which defines said passage and a shell having a tubular portionsurrounding said upper chamber, said member being disposed substantiallytangentially of said tubular portion.
 17. The apparatus of claim 16,wherein said member is disposed in said upper chamber.
 18. The apparatusof claim 16, wherein said member is adjacent said tubular portion. 19.The apparatus of claim 13, further comprising means for diverting atleast some dispersion from said conduit into at least one of saidchambers.
 20. The apparatus of claim 19, wherein said diverting meanshas an outlet adjacent said partition.
 21. The apparatus of claim 13,wherein said conduit includes an upright pipe and said vessel furthercomprises a shell substantially concentrically surrounding said pipe.22. The apparatus of claim 13, wherein said damming means includes a topwall and said intake is disposed beneath said top wall.
 23. Theapparatus of claim 22, wherein said conduit has a nipple which definessaid intake.
 24. The apparatus of claim 23, wherein said nipple isdisposed substantially tangentially of said conduit.
 25. The apparatusof claim 13, wherein said upper portion includes an enlarged receptacleabove said damming means, said conduit including an upper end portionextending into said receptacle upwardly and beyond said damming meansand having an open top to permit the dispersion to overflow into saidreceptacle, said outlet being provided in said receptacle at a levelbelow the open top of said upper end portion.
 26. The apparatus of claim13, wherein said vessel further comprises a shell which spacedlysurrounds said conduit, said partition being sealingly secured to saidconduit and to said shell.
 27. The apparatus of claim 13, wherein saidadmitting means includes means for maintaining the dispersion in theregion of said damming means at a speed of approximately ten meters persecond.
 28. The apparatus of claim 13, further comprising carriermaterial for microorganisms in at least one of said chambers.
 29. Theapparatus of claim 28, wherein said admitting means includes means forinducing the flow of dispersion at a speed such that the carriermaterial remains in said one chamber while being contacted by thecirculating dispersion.